Drop the volume New Zealand Safety Week

Key facts about noise induced hearing loss

The more time a person’s ears are exposed to excessive noise, the greater the degree of hearing loss. More time equals more acoustic energy and hence more damage.

The damage that results is irreversible, and treatment is limited.

Regulation 11 of the Health and Safety in Employment Regulations 1995 states the levels of noise exposure that should not be exceeded. There are two exposure limits – an “average” level (over 8 hours) of 85dBA, and a “peak” level of 140dB.

The human ear is not particularly good at detecting the differences in volume, particularly at higher sound levels. By way of example, a sound level of 97dB (Average) – not unusual in nightclubs – delivers twice as much energy to the ear as one of 94dB (Average), yet it doesn’t appear twice as loud.

Current ACC statistics indicate that total costs of noise induced hearing loss to New Zealand exceeds $40 million per year (double that of 5 years ago).

About 4000 new serious injury claims are made to the ACC annually, which is 11 new claims for every day.

Noise induced hearing damage appears in the top 5 of all claims.

People suffering from occupational deafness experience a distortion of the sounds they hear, as they lose the ability to hear at some speech frequencies. In particular, the ability to hear consonant sounds such as t, k, s, sh and p is reduced, and people can no longer distinguish between some words, or indeed what is being said.

Hearing aids offer very limited benefit for some people with noise-induced hearing loss.

Performance in reading, writing and listening tasks is affected by noise. These tasks, and those requiring a steady posture, are also disrupted, particularly by sudden bursts of noise.

Many common drugs are recognised as affecting the inner ear and the hearing mechanism (these are known as ototoxic drugs). One of these is alcohol. Ototoxic drugs can interact with noise to compound its effects on hearing. This is why people often need to shout in bars – the hearing of people who have been drinking is impaired.

Other ototoxic substances include many common antibiotics, nicotine, carbon monoxide, some diuretics and analgesics.

Exposure to some hazardous substances can also damage peoples hearing. The way it affects a person’s hearing is different to noise induced hearing loss, but the consequences for the person are the same.

Chemicals that can contribute to hearing loss include: solvents such as toluene, styrene, xylene, n-hexane, and ethyl benzene; asphyxiants such as carbon monoxide; metals such as lead and mercury; and pesticides such as organophosphates.